The present invention relates to a wavelength selective filter for tuneable filtration of one or more wavelength channels from a stream of Q-number of wavelength channels and to a method for wavelength selective filtering of a wavelength channel from a stream of Q-number of wavelength channels.
There are known to the art a number of different methods by means of which the capacity of an existing optical network can be further increased. One method is to use so-called wavelength multiplexing technology (WDM) to improve the extent to which an available bandwidth can be exploited on an optical fibre in the optical network.
Wavelengths can also be used as an information address in an optical network, that is to say information can be multiplexed on a number of channels and these channels treated individually in the network. It may also be desirable to redirect traffic in the optical network. Filtering may be necessary in order to reduce crosstalk, for instance immediately upstream of an optical receiver (detector). A tuneable filter may be required to enable selection of an optical detection channel.
Tuneable filters according to the present standpoint of techniques generally have one or more of the following drawbacks.
Relatively high losses in respect of desired channels, and poor suppression of other channels.
Reflections in the device, which may be a problem to the transmission system as a whole.
An excessively pointed filter profile (not system-friendly).
Expensive devices.
Tuning is only possible over a narrow wavelength band.
An object of the present invention is to at least reduce these problems.
According to a first aspect of the invention, there is provided a wavelength selective filter for tuneable filtration of a wavelength channel from a stream of Q-number of wavelength channels. The filter includes one or more wavelength selective add-drop elements and one or more on-off switches wherein a first and a second side of the wavelength selective add-drop elements include an input and an output, wherein said on-off switches are disposed between said input and output on said second side of said wavelength selective add-drop elements. In the event of more than one wavelength selective add-drop element, said elements are interconnected by a connecting waveguide between respective outputs and inputs on the first side of the wavelength selective add-drop element.
According to another aspect of the present invention, there is provided a wavelength selective filter for tuneable filtration of one or more wavelength channels from a stream of Q-number of wavelength channels. The filter includes one or more devices for filtering out a specific wavelength channel, wherein each device includes an input and an output, a part through which solely said specific wavelength channel passes through and which includes at least one on-off switch which when in an off-mode prevents said specific wavelength channel from passing through said device for filtering out a specific wavelength channel. In the event of more than one device for filtering out a specific wavelength channel, said devices are interconnected by a connecting waveguide between the output of one device and the input of the other device, so as to enable several channels to be filtered out independently of each other.
According to another aspect of the present invention, there is provided a method for wavelength selective filtering of a wavelength channel from a stream of Q-number of wavelength channels. The method comprises inputting optical wavelength channels on an input provided on a first side of a first wavelength selective add-drop element and reflecting a specific wavelength channel and thereafter outputting said channel on an output provided on said first side of said wavelength selective add-drop element. The method also comprises outputting wavelength channels that are transmitted through said add-drop elements on an output provided on a second side of the add-drop element and blocking said wavelength channels or feeding said channels back to an input provided on said second side of the add-drop element. The method further comprises transmitting said fed-back wavelength channels through the add-drop element and outputting said channels on the output on the first side of said add-drop element and coupling the wavelength channels from the output on the first side of the add-drop element with an input on a first side of a second add-drop element and thereafter repeating the same procedure in respect of said add-drop element and the N-number of subsequent add-drop elements.
One advantage afforded by the present invention is that it improves performance with respect to crosstalk and the like, when seen in perspective with known techniques.
One advantage afforded by the preferred embodiments of the present invention resides in enabling tuning to be achieved over a relatively wide wavelength range.
So that these and other advantages will become more apparent, the invention will now be described with reference to preferred embodiments thereof and also with reference to the accompanying drawings.